Field of the Invention
The present invention provides a nozzle plate and use of the nozzle plate for producing continuous filaments, preferably silica gel fibers.
Description of Related Art
Patent DE19609551C1 and published patent application DE102004063599A1 disclose a method for producing silica gel fibers. The method comprises a plurality of steps. In a first step, a spinning composition is produced which, in a second step, is pressed from a pressure vessel through nozzles, where it emerges in the form of filaments. Depending on the size of the nozzles, the filaments have a diameter of approx. 10 to 100 μm.
Published patent application DE102004063599A1 discloses details regarding the nozzles through which the spinning composition is pressed. A 7- or 19-hole nozzle plate is used. The drill bore leading up to a hole is 3.0 mm wide and the hole diameter D amounts to 0.15 mm. At a capillary length L of 0.45 mm, an L/D ratio of 3 is obtained. FIG. 2 of the published patent application shows a schematic diagram of the nozzle plate and an individual hole-type nozzle in cross-section.
This nozzle plate described in the prior art exhibits disadvantages. At the start of a pressing operation of the spinning composition through a nozzle as disclosed in DE102004063599A1, the emerging spinning composition wets the planar zone around the nozzle orifice. Spinning composition collects around the orifice until, under the effect of gravity, it gradually becomes detached from the nozzle orifice and falls to the ground in the form of a drop which takes a spun filament with it.
The individual nozzles here exhibit a different behavior over time. There are individual nozzles from which a filament immediately emerges, the thickness of which is, however, initially nonuniform, since some of the emerging spinning composition sticks behind on the region around the nozzle orifice and, apart from a thin film, only becomes detached from the nozzle plate after varying lengths of time. There are individual nozzles for which the filament breaks off and only forms a new uniform filament once a certain amount of time has elapsed. In addition to the nonuniformity, the spinning composition located in the region around the nozzle orifice may impair filament formation during the entire spinning procedure if said spinning composition only becomes very incompletely detached from the nozzle plate and the composition which is left behind comes into contact with the filament. This may give rise to disruption of filament formation and movement which may go as far as a plurality of filaments becoming tangled or the periodic formation of drops.
These problems result, for example, in its being necessary to discard the filaments which initially emerge from the nozzles due to their nonuniformity. If the method for producing filaments is interrupted, uniform filaments can only be produced again after a significant startup time and elaborate cleaning of the nozzle plate. It is here very often observed that spun material, which inevitably remains behind as a thin film around the nozzle opening after detachment of the spinning composition from the nozzle plate, leads to spinning composition only becoming very incompletely detached from the nozzle plate when the spinning operation is restarted, such that the nozzle plate must first be cleaned before it can be used again.
On the basis of the described prior art, a person skilled in the art is therefore faced with the problem of finding a solution to the adhesion of spinning composition at the nozzle orifices and the concomitant initial formation of nonuniform filaments. The solution is in particular intended to be suitable for the production of silica gel fibers.